A technique was disclosed in U.S. Pat. No. 4,958,919 to R. D. Sigler for designing lens systems with reduced secondary spectrum using liquid refractive elements in combination with rigid (e.g., glass, plastic or crystal) refractive elements. Lens elements consisting of certain abnormally dispersive liquids can be used in combination with lens elements made of certain ordinary (i.e., relatively inexpensive) optical glasses of normal dispersion to achieve reduced secondary spectrum. In manufacturing optical systems, it is generally more economical to use liquid lens elements of abnormal dispersion instead of exotic glass lens elements of abnormal dispersion.
In fabricating a lens system in which a liquid lens element is to be confined within a gap between two glass lens elements, the glass lens elements must be mounted so as to seal the liquid lens element within the gap. In co-pending patent application Ser. No. 07/941,299 by D. F. Leary, filed on Sep. 4, 1992, a proprietary fluorosilicone compound marketed by Dow Corning Corporation of Midland, Mich. under the trade designation "DOW CORNING X5-8738" was disclosed as being particularly advantageous for use as an adhesive sealant in fabricating lens systems comprising liquid lens elements. The "DOW CORNING X5-8738" compound has been found to form a seal that remains leak-tight when exposed to silicon oils, esters, aldehydes, ketones, aromatic hydrocarbons and aliphatic hydrocarbons over a temperature range extending from -40.degree. C. to 60.degree. C. for a period of time longer than 24 months.
In manufacturing lens systems such as telescope objectives on a mass-production basis, where liquid lens elements are to be contained between glass lens elements, it is necessary to use a mounting technique whereby the glass lens elements can be positioned coaxially with respect to each other with extremely accurate precision, and whereby the liquid (or liquids) comprising the liquid lens elements can be contained within gaps between adjacent glass lens elements without leaking from the gaps.